This invention relates to a process for preparing a silver-supported catalyst for the production of ethylene oxide. More specifically, it relates to a process for preparing a silver-supported catalyst which when used in the catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas, can afford ethylene oxide with a high level of catalytic activity.
Catalysts for use in the commercial production of ethylene oxide by catalytic vapor phase oxidation with molecular oxygen are required to have a long catalytic lifetime in addition to a high activity and selectivity. Many silver-supported catalysts have been suggested heretofore in an attempt to improve these properties. For example, the inventions disclosed in British Pat. Nos. 1,300,971, 1,020,759, and 1,413,251, U.S. Pat. No. 3,702,259, and British Pat. No. 1,489,335 are known. These patent documents disclose that a silver-supported catalyst is prepared by depositing silver or a silver compound together with an alkali metal compound, an alkaline earth metal compound or another metal compound as a promoter on a suitable inorganic carrier by a coating method or impregnating method, and then reducing or heat-treating the product. Such known catalysts attain industrially required levels of conversion of ethylene and selectivity to ethylene oxide, but are still not satisfactory and require further improvement with regard to the method of supporting silver or a silver compound, the selection of the promoter, the method of adding the promoter, the selection of the carrier, and the method of activating the catalyst. For example, the catalytic activity of supported metallic silver is greatly affected by the method of preparing metallic silver, the method of its supporting, the method of activation, etc. The reducing treatment and heat-treatment at a temperature of 250.degree. C. or higher and at times more than 300.degree. C. which are suggested in these documents as improved methods never give stable highly active silver, and moreover involve a danger of explosion and combustion. The type of the promoter compound, the time of its addition and the method of its addition markedly affect the activity of the resulting catalyst. Further, the properties of the carrier, i.e. the specific surface area, the pore distribution, etc. greatly affect the activity or selectivity of the catalyst.
It is an object of this invention therefore to remedy these defects of the prior art in silver-supported catalysts.